The China Ore-Dressing Equipment Manual published by the Science Press in 2006 describes a vertical grinder in page 407, and a grinding device of the vertical grinder is illustrated in FIG. 1, including a driving device 1′; a vertical grinding barrel 2′ which is driven by the driving device; a grinding roller 3′; and a pressure applying device 4′ acting on the grinding roller 3′; wherein the vertical grinding barrel 2′ is located in a body casing 5′; and a running-in surface is composed of the roller surface of the grinding roller and the grinding surface 6′ of the inner lining of the vertical grinding barrel. Materials enter the vertical grinding barrel through a material inlet 7′. The driving device drives the vertical grinding barrel to rotate, and the grinding roller rotates therewith, so as to grind the materials entering the running-in surface. The grinded materials are thrown off the vertical grinding barrel under the centrifugal force caused by the rotation of the vertical grinding barrel 2′. The fine-particles of the grinded materials are discharged with an airflow rising from the lower portion, and uncrushable materials such as tramp iron is discharged from a slag outlet 8′ at the lower portion of the body casing. The grinding device has the following disadvantages: since the vertical grinding barrel 2′ is of a bowl-shaped structure and the grinding surface 6′ of the inner lining of the grinding barrel forms a large angle with the vertical line (i.e., the grinding surface 6′ is relatively horizontal), the grinded materials are thrown off the grinding barrel under the centrifugal force at a fast speed and cannot be controlled, and thus they are being freely discharged; particularly, when the vertical grinding barrel 2′ rotates at a high speed, a large centrifugal force is generated, the materials stay on the running-in surface only for a short time, and the times of crushing and grinding the materials are reduced; therefore, the grinding production efficiency is low and the energy consumption is high; when the grinded materials contain too much moisture, the materials may be attached to the vertical grinding barrel and form a massive layer due to absence of a material-shaving device, which further affects the yield.